shockmetamorphosed

Shockmetamorphosed refers to rocks that have been altered by shock metamorphism, a type of metamorphism produced by the passage of intense, short-lived shock waves through a rock. This condition is most commonly associated with meteorite impacts but can also occur in association with underground nuclear explosions or large volcanic explosions in rare instances. The rapid compression and subsequent decompressional expansion drive mineralogical and textural changes that differ from slower, temperature- and pressure-driven regional metamorphism.

Key diagnostic features include planar deformation features PDFs in minerals such as quartz and feldspar, the formation of diaplectic glass such as maskelynite, and the presence of high-pressure polymorphs such as coesite and stishovite in quartz-bearing rocks. Shatter cones, cup-shaped fractures formed by localized stress, are characteristic surface indicators of shock metamorphism. Melt rocks and glass spherules, produced by localized melting, are also common at impact sites.

The intensity of shock metamorphism ranges from low to extreme, affecting the mineral assemblage and textures. Low-to-moderate shock may produce PDFs without significant phase changes; higher shock yields diaplectic glass and high-pressure minerals; the highest pressures can generate full melts and impact breccias. The occurrence is typically within impact structures like crater rims, breccias and impact melts known as suevite, or in ejecta deposits such as tektites.

Examples of well-studied shockmetamorphosed rocks occur at major impact structures such as the Barringer Meteor Crater in Arizona, the Ries crater in Germany, the Sudbury Basin in Ontario, and the Chicxulub crater in Yucatán. The study of these rocks helps determine the pressures, temperatures, and timescales of impact events and supports the identification and dating of meteorite impacts in the geological record.